Sarah "Queen of Blades" Kerrigan is one of the main characters that the player will encounter in the StarCraft II Trilogy and be able to control in StarCraft II: Heart of the Swarm (the second game in the SC2 trilogy). Driven by vengeance, having both Terran intellect with strong psychic powers and overwhelming Zerg brutality, Kerrigan will be a hard nut to crack.
Before the game
Brought into the Confederate Ghost program as a child, Kerrigan was never given the chance for a normal life. The neural processing treatments that were used to dampen and pacify her latent psychic powers left her a withdrawn and introverted young girl. Forced to murder countless enemies of her Confederate masters, Kerrigan was finally exposed to a series of clandestine experiments conducted by the Confederate Government. During a raid on a remote Terran outpost, Arcturus Mengsk discovered and rescued Kerrigan from the Confederate scientists. The Confederates had ruined both their lives, and it was a simple matter to convince the young woman to lend her formidable combat skills to his cause. Although Kerrigan is often called upon to be an executioner, she has never fully embraced the darker aspect of her true nature
Saved by Arcturus Mengsk from Confederacy control as a Ghost, Sarah Kerrigan joined the Sons of Korhal rebel force. Showing courage and being a successful tactician, Kerrigan became second in charge under Mengsk's command.
During the revolution on Antiga Prime, Kerrigan and Jim Raynor (who felt strong sympathy to her, or perhaps more) successfully freed the colony by exterminating key local Confederate forces. As the conflict evolved, aliens called the Zerg infested the planet. Mengsk, looking for a possible advantage of the situation, tasked Kerrigan to place a Psi-Emitter (a device stolen from the Confederacy, which was believed to have the power to lure Zerg colonies across planets) in a Confederate base. Swarms of Zerg slaughtered the Confederate positions and Kerrigan left with disgust, seeing the massacre she caused.
The Sons of Korhal's next move was an assault on Tarsonis (the capital planet of the Confederacy). Even after defeating the Confederate forces, Mengsk gave the order to plant Psi-Emitters. After an endless number of Zerg reached the planet, Protoss forces entered the system, trying to destroy the Zerg infestation on Tarsonis. Arcturus Mengsk, after witnessing this turn of events, sent Kerrigan on a suicidal mission to protect the Zerg Hive from Protoss attack, which she completed. However, after an urgent call for escape, she was abandoned on the planet on Mengsk's orders. Perhaps, after feeling the taste of power, he saw Kerrigan as a huge threat to his future plans. Jim Raynor and his squad deserted the Sons of Korhal afterwards.
Kerrigan was captured by the Zerg, and put in a special incubator called the Chrysalis on the planet Char. Trapped in her darkest nightmare, Kerrigan was slowly mutating into the most powerful weapon of the Zerg - the Queen of Blades. Using her telepathic powers, she was desperately calling Raynor for help. Unfortunately, Raynor was too slow making his way across Char and arrived too late. The Chrysalis had completed its work and the Queen of Blades was born.
"The Queen of Blades stared at her would-be savior with a cold look. She was not Kerrigan any more; her body had changed dramatically: her skin had become mottled, she had grown a protective carapace, her hair resembled snakes, andd she had grown a pair of featherless wings, used as melee weapons. Only her human stature, face, ability to talk, human intelligence, psionic abilities, and memories were still remaining. Since Raynor didn't present any threat to her, she let him go unharmed."
While she obeyed the Overmind and certain Cerebrates, Kerrigan was able to make her own decisions, and her mind was not fully controlled like other Zerg minions - the Overmind believed her fierce spirit would set an example for the rest of the Zerg. Shortly after her new appearance, the Queen of Blades demanded they let her infiltrate a Terran Science Vessel - the Amerigo, to find out more about the secrets of Terran Ghost training. Afterwards, Kerrigan developed many abilities, such as Psionic Storm, and could sense the Protoss presence on Char. She sensed and chased Tassadar on the planet, but he was a decoy to take her attention from the Protoss Dark Templar Zeratul. As a result, Zeratul killed the Cerebrate Zasz. But when Zeratul stabbed Zasz with his Psi Blades, the Overmind telepathically discovered Aiur, the Protoss homeworld's location, and sent the majority of the Zerg forces to invade. Kerrigan was left on Char to fight the remaining Protoss and Raynor's Raiders. During the Aiur invasion, the Overmind was destroyed, and Kerrigan started gaining control of the majority of the Zerg forces, building up a plan to avenge what happened to her during the events on Tarsonis.
During the Brood War, the Queen of Blades had under her control half of the Zerg forces. Daggoth and other Cerebrates, seeing that they were losing control of the Swarm, merged into a new Overmind. Kerrigan traveled to the distant Protoss planet Shakuras, home of the Dark Templars, and through mind control, took over the Dark Templar's queen, Raszagal. Allied with Daggoth, Kerrigan approached the Protoss leaders after retaking a Xel'Naga Temple from two Cerebrates. With the help of the infested Raszagal, she manipulated them, claiming she was not under the Overmind's control, and offered an alliance to kill all her rivals in the Swarm. As a result, all Cerebrates who refused Kerrigan's leadership were exterminated. However, the Dark Templar Zeratul didn't trust her and refused to kill the new Overmind.
Using the newly arrived United Earth Directorate's (UED) plans to take control of the new Overmind to threaten to all of the rival factions, Kerrigan made an alliance with Mengsk, Raynor, and the Protoss hero Fenix. Kerrigan also had an Infested agent in the UED named Samir Duran, who sabotaged the UED from the inside. After a successful battle on Korhal, the Queen of Blades betrayed her allies - while they were resting, she attacked the allied forces, killing Fenix and Mengsk's key generals.
Shortly after that, Kerrigan 'captured' Raszagal on Shakuras and blackmailed Zeratul - if he won't kill the new Overmind, he would never see his queen again. After struggling between the two impossible choices, Zeratul's and Kerrigan's forces killed the new Overmind and the remaining Cerebrates. Unfortunately, Kerrigan had full control over Raszagal, and the queen of the Dark Templar refused to leave. Zeratul imprisoned Raszagal in a Stasis Cell, hoping to heal her. Shortly afterward, Kerrigan launched her forces against the Dark Templar and faced Zeratul in front of the Stasis Cell. Watching helplessly as Zeratul killed Raszagal, Kerrigan let him go, saying she wanted him to suffer being alive with the guilt of what he has done.
At the very end of the Brood War, the Queen of Blades and her forces faced one final attack from the UED remains, a Protoss fleet and the mercenary fleet commanded by Mengsk. And again, the Zerg, led by Kerrigan, completely crushed all her enemies, even though for once numerical superiority was on the opposing side. Making Kerrigan the most powerful leader in the galaxy, but also the most hated and the most feared.